1. Field of the Invention
This invention generally relates to devices for measuring relative hydration of a substrate, such as hydration of the human skin or physical substrate materials.
2. Description of Related Art
There is a growing interest in measuring the relative hydration of a substrate. For example, such measurements on human skin provides information about wound healing. Measurements on hydration through films, such as bandages and tapes, can indicate the efficacy of certain compositions of such bandages or tapes in connection with the healing process.
A number of devices exist for measuring relative hydration of human skin by measuring the water content of the skin typically by measuring skin impedance. For example, U.S. Pat. No. 5,961,471 issued Oct. 5, 1999 by Steven W. Nickson for a probe for a biophysical skin measurement device discloses one such device for measuring relative skin hydration that has received wide acceptance.
It has been recognized that variations in the force at which such a probe is applied to the skin can affect the measured impedance. For example, U.S. Pat. No. 5,001,436 (1991) to Scott et al. discloses a skin impedance measuring device that recognizes a necessity for some method of controlling the pressure applied. Scott et al. monitor the force applied by the probe and trigger the measurement when an acceptable force exists. U.S. Pat. No. 5,588,440 (1996) to Cowie discloses a system for measuring skin temperature and measuring force. However, the force measurement merely provides an indication of the force as a guide for helping the user control the force at which measurements are taken. In both disclosures it becomes incumbent on the operator to control the force manually in order to obtain sustained measurements.
Notwithstanding these attempts to compensate for temperature and force in skin moisture measurement devices, there is still a requirement for a relative hydration measuring system that will automatically compensate for the effects of force and temperature variations during the measurement process.
Therefore it is an object of this invention to provide a relative hydration measuring device and method that can compensate for the force applied by a measurement probe.
Another object of this invention is to provide a relative hydration measuring device and method that can compensate for the temperature of the substrate being tested.
Yet another object of this invention is to provide a relative hydration measuring system for human skin that automatically produces a moisture indication that can be compensated for probe force and skin temperature during the measurement.
In accordance this invention, relative substrate hydration is obtained by measuring the electrical characteristics of the substrate between electrodes contacting the substrate and by measuring concurrently an environmental factor. These measurements provide the basis for obtaining a value of substrate impedance between the electrodes that indicates relative hydration.
In accordance with another aspect of this invention, a system for measuring the relative hydration of a substrate comprises a probe having first and second electrodes for contacting the substrate. An electrical impedance measurement circuit periodically generates a value representing the impedance of the substrate between the first and second electrodes. An environmental factor measurement circuit periodically generates a value representing an environmental factor associated with the impedance measurement. A calculator may respond to the impedance and environmental factors signals to produce an indication of relative hydration.
In accordance with yet another aspect of this invention, a system for measuring the relative hydration of a substrate includes a measurement probe and a data processing system. The measurement probe comprises an elongated probe housing and a sensor body mounted at one end of the probe housing with first and second concentric electrodes for contacting the substrate at a site for which a relative hydration measurement is desired. An electrical impedance measurement circuit in the probe housing generates an impedance signal including information about the capacitive reactance between the first and second electrodes. A force sensor in the probe housing generates a signal representing the force exerted by one of the electrodes on the substrate. A signal processor in the probe housing polls the electrical impedance measurement circuit and the force sensor thereby to generate processed impedance and force measurement signals. A connector at the other end of the probe housing enables communications between the data processing system and the signal processor.
In accordance with still another aspect of this invention, a system for measuring relative hydration of a substrate includes a measurement probe and a data processing system. The measurement probe comprises an elongated probe housing and a sensor body mounted at one end of the probe housing with first and second concentric electrodes for contacting the substrate at a site for which a measurement of relative hydration is desired. An electrical impedance measurement circuit in the probe housing generates an impedance signal representing the impedance of the substrate between the first and second electrodes. A temperature sensor in the probe housing generates a signal representing the temperature of the skin contacting the electrodes. A signal processor in the probe housing polls the impedance measurement circuit and the temperature sensor thereby to generate processed impedance and temperature measurement signals. A connector at the other end of the probe housing enables communications between the data processing system and the signal processor.